Explosive compositions



. kind. It is, known,

However,

United States Patent-O 2,829,958 nxrLosrv-n COMPOSITIONS Samuel; Henry Davidsom Largs, Scotland,'and Thomas Balfour, Northrand, Union of South Africa, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great. Britain No Drawing. Application A ia s, 1955 seiiaiNasoagm Claims priority, application Great Britain April 26, 1954 sciaims. c1. s2 e7- The present invention is concerned with new'and improved ammonium nitrate explosive compositions of the kind which are safe for use in methaneairmixt ures and which would be regarded as permitted orpe'rmissiblc however, always available and their manufacture involves a hazard additional to. that associated with their mixing with the other ingredients oi the final explosive composition. Furthermore the ammonium nitrate which is-used is of the usual grist size and usually cannotfbe made'to explode in cartridges of the" general: nature and size re l of the aforesaid howeyer thatt a mixtureof ammosize as ordinarily used in the manuquired to attain explosive compositions.

niuminitrate. of grist facture of explosive density, as'for example balsa meal, cork dust and bagasse. explosive compositions of unusually low bulk density tend to become compacted during transport to a higher density withan adverse elfect' on their sensitiveness a i iati n a pmpa Although explosive compositions have been proposed for coal-mining which contain aluminium as an ingredient, as a result of increasingly stringent requirements in recent years in respect of freedom from danger in igniting methane, including for instance the introduction of ofiicial Gallery tests, no explosive composition containing aluminium as an ingredient has appeared for several years in the olficial list of explosives permitted for use in coal-mines for exampleby H. M. Home Office.

The object of the present invention is to provide explosive compositions for use in gassy or fiery mines which are free from self-explosive ingredients and have a satisfactory sensitiveness to initiation and capacity for propagation and bulk densities in a range high enough to be maintained during transport and a greater strength than any that have hitherto been found safe enough for use in gassy or fiery mines.

An explosive composition according to the invention comprises ammonium nitrate of particle size such that substantially all of it passes a 120 B. S. S. sieve, aluminium particles such that at least a part is paint-fine, vegetable tissue material, and at least one flame-quenching ingredient, and has a bulk density not less than 0.85 g./cc. and not greater than 1.1 gJ/cc. and is substantially oxygen balanced. I

The power of the explosive compositions of the invencompositions and aluminium powder i can be caused toexplode by means of a commercial detodiatom-if the'densityof the mixture is suitably diminished the inclusion therein of dry vegetable tissue. These yegetabletissue materials are specially eifective in facilitat inginitiation when they are of intrinsically lowbulk aluminium particles,

tion should preferably be less than 74% blasting gelatine.

may include organic ingredients for instance orthonitro toluol.

Examples of flame-quenching ingredients are sodium chloride, sodium sulphate' and china clay. If sodium chloride 'is the flame-quenching ingredient the quantity present should be at least 8% and preferably not more than 25%. n

Preferably the ammonium nitrate in the compositions of the invention. is of particlesize such that not less than 60% passes a No. 240 B. S; S. sieve, not less than passes a No. 170 B. S. S. sieve and substantially all, i. e, at least 98%, passes a No. B. S. S. siev It is also preferred thatthe total amount of aluminium in the composition be not less than 1%. and not more than 25% byxweight and that not less than 0.5% and not more than 1% of the aluminium present based on the'weight of the explosive composition be paint-fine aluminium.

Furthermore a composition of the invention is satisfacexplosive compositions of the same percentage composition and power, the improvement is still insuificient to enable the whole of the oxidisablecontent of the explosive composition to consist of aluminium. Again although ,thesensitising effect on ammonium nitrate of paint-fine aluminium is higher than that of granular aluminium the tendency of paint-fine aluminium to ignite methane-air mixtures is higher than that of granular aluminium and so the percentageof paint-fine aluminium that may be present in an explosive composition is even more severely limited than that of granular aluminium. Therefore, to achieve the desired sensitiveness to initiation and propagation of an explosive composition comprising ammonium nitrate in finely divided form and at least part of which is paint-fine, it. is essential to include at least a portion of the remainder of the oxidisable ingredients to make thecomposition oxy'genjfbal'anced in the form of vegetable tissue material. Such material has the efiect furthermore of reducing the density of the composition more thanordinary oxidisable than 1.1 g./cc; if satisfactory sensitiveness to initiation and propagation is to be achieved. On the other hand it is undesirable that the density should be lower than 0.85 g./cc. Examples of vegetable material suitable for use in the compositions of the invention are woodfiour, which has a density of about 0.4 g./cc., or lower density materials as for instance balsa meal, ground cork or bagasse.

Ammonium nitrate as heretofore employed in explosives suitable for fiery or gassy coal-mines consists of crystal clusters or crystals of such size as to be substantially retained on a No. B. S. S. sieve and is inefiective forthe present invention tween 0.85 and 1.1 g./cc. mixtures of the same percentage compositions' containing such ammonium nitrate in place of the fine ammonium nitrate used in the compositions of the present invention are insensitive to commercial detonators and require the use of abooster the employment of whichis not permitted in, commercial coal-mining practice. 7

The invention is illustrated by compositions Nos. 1 to Sand compared with compositions Nos. 6 to 9 not in accordance with the invention in the following table.

Nine explosive compositions are made by mixing together the ingredients as shown in the following table and are formed into cartridges of the sizes normally required Thus at bulk densities bea 3 for coal-mining. These ance with two Gallery tests. In accordance with one Gallery test it is not permissible to get a failure when five shots of 8 oz. each are fired from a mortar unstemmed in a Gallery containing 9% methane in 'a mixture of methane and air. In accordance with the second Gallery test five shots of 28 oz. stemmed with a 1 inch thick dry clay plug when fired into a Gallery containing 9% methane in a mixture of methane and air must not ignite the gas. The ammonium nitrate which is used in the nine explosive compositions is of particle size such that 80% by weight passes a N0. 240 B. S. S. sieve and all of it passes a No. 120 B. S. S. sieve.

Ammonium nitrate of the usual commercial size, i. e. one wherein only 20% passes a No. 120 B. S. S. sieve and only 75% passes a No. 60 B. S. S. sieve when used to make the explosive compositions indicated in the following table produce explosive compositions of such reduced sensitiveness that they fail to fire when formed into cartridges of the ordinary commercial size for use in bore holes in mines when any commercial detonator is used.

cartridges are tested in accordpasses a No. 240 B. S. S. sieve, not less than 80% thereof passes a No. 170 B. S. S. sieve and substantially all thereof passes a No. 120B. S. S. sieve, from 1% to 2.5% of aluminum particles by weight of total composition wherein 0.5% to 1% of said particles by weight of total composition are of a pigment powder fineness, vegetable tissue material and at least one flame-quenching ingredient, and having a bulk density not less than 0.85 gram per cc. and not greater than 1.1 grams per cc. and being substantially oxygen balanced.

2. An explosive composition as claimed in claim 1 which includes organic ingredients.

3. An explosive composition as claimed in claim 2 wherein the organic ingredient is orthonitrotoluol.

4. An explosive composition as claimed in claim 1 wherein said flame-quenching ingredient is selected from the group consisting of sodium chloride, sodium sulphate and china clay.

5. An explosive composition as claimed in claim 4 wherein the quantity of sodium chloride is between 8% and 15%.

ammonium nitrate thereof 74%blasting gelatine and comprising of particle size such that not less than 60% Composition (parts) Properties Gallery tests Composition Ammo- Paint- Granular Oxygen Power Initia- No. nium fine alumln- O-nitro- Bagasse Sodium surplus, Density, (percent tion by l 2 nitrate alumin- 111m toluol chloride g. 02/100 g./e.e. Bl detonaium g. tor No.

5 1. 2 1. 10 71. 8 6 8-12 30 8 8 +4. 9 1. 04 68. 1 5 12 30 8 15 3. 5 0. 86 63. 0 4 12 30 10 18 0 0. 85 58. 9 3 12 30 8 5. 0 0. 93 51. 2 5 12 4 e -0. 1 0. 94 74. 5 6 8 28 8 +2. 0 0. s5 s0. 3 4 8 28 4 +2. 1 1. 02 82. 0 5 8 28 8 26 -5.5 0.92 51.8 8 12 30 From the table it will be seen that compositions Nos. References Cited in the file of this patent 1 to 5 and 9 pass both Gallery tests but composition No. UNITED STATES PATENTS 9 which is not within the invention as it has no paint- 40 fine aluminium, is unsatisfactory because its sensitiveness 1,891,500 Burrows 1932 is so low that a No. 8 detonator is required for its initia- 1972681 FOX 6i 193-4 tiom 2,398,071 Barab Apr. 9, v1946 There is no correlation between the power of any one 2,409,919 Whetstone 1946 of said explosive compositions and its sensitiveness. To 2,613,146 Lowe 1952 be satisfactory asa blasting explosive, however, it must FOREIGN PATEN IS be gg g by a 6 weakerrdemnawr- 649,473 Great Britain Jan. 24, 951 1. An explosive composition having a power less than OTHER REFERENCES Serial No. 393,137, Baron (A. P. C.) published Jun 15,1943. 

1. AN EXPLOSIVE COMPOSITION HAVING A POWER LESS THAN 74% BLASTING GELATINE AND COMPRISING AMMONIUM NITRATE OF PARTICLE SIZE SUCH THAT NOT LESS THAN 60% THEREOF PASSES A NO. 240 B.S.S. SIEVE, NOT LESS THAN 80% THEREOF PASSES A NO. 170 B.S.S. SIEVE AND SUBSTANTIALLY ALL THEREOF PASSES A NO. 120 B.S.S. SIEVE, FROM 1% TO 2.5% OF ALUMINUM PARTICLES BY WEIGHT OF TOTAL COMPOSITION WHEREIN 0.5% TO 1% OF SAID PARTICLES BY WEIGHT OF TOTAL COMPOSITION ARE OF A PIGMENT POWDER FINENESS, VEGETABLE TISSUE MATERIAL AND AT LEAST ONE FLAME-QUENCHING INGREDIENT, AND HAVING A BULK DENSITY NOT LESS THAN 0.85 GRAM PER CC. AND NOT GREATER THAN 1.1 GRAMS PER CC. AND BEING SUBSTANTIALLY OXYGEN BALANCED. 